Technical Field
This disclosure relates to the field of wireless communications, including multicast in multi-user transmissions in a wireless local area network (WLAN).
Background
A wireless communication protocol may support multicast transmission. For example, the Institute of Electrical and Electronics Engineers (IEEE) 802.11ax standard (current proposals and/or future versions) supports multicast transmission. In a multicast transmission, an access point (AP) may transmit a frame to a group of stations who have joined a multicast group. This is in contrast to a broadcast transmission where an AP transmits a frame to all stations in a wireless local area network (WLAN), or a unicast transmission where an AP transmits a frame to a single station in the WLAN.
A multicast transmission is an efficient way to transmit a large amount of data (e.g., real time audio and video) to a group of stations in a WLAN. A multicast transmission may be more efficient than a unicast transmission because an AP only has to generate a single frame, and this single frame can be simultaneously sent to all stations in a multicast group. In contrast, in a unicast transmission, an AP has to generate a separate frame for each station. Thus, a multicast transmission is often more efficient than a unicast transmission in terms of bandwidth conservation.
A multicast transmission is similar to a broadcast transmission. Both involve the transmission of a frame to multiple stations. However, receiving stations may handle multicast and broadcast transmissions differently. Specifically, because a broadcast transmission is intended for all stations in a WLAN, all stations need to remain awake and decode the entire frame. In contrast, a multicast transmission is often intended only for a group of stations in a WLAN. Therefore, a power saving opportunity exists for other group addressed stations not in a particular multicast group. Specifically, a station in one multicast group does not need to stay awake to decode a multicast frame that is not destined for the station. Because the station does not need to decode the multicast frame, the station avoids performing decode processing which reduces power consumption.
But often a station in one multicast group may need to stay awake to decode a multicast frame not destined for the station. This is because the multicast frame may be included in a multiuser physical layer protocol data unit (MU-PPDU) frame along with one or more frames that are destined for the station. In other words, a MU-PPDU frame may include one or more subframes, and a portion of the subframes may be destined for the station and a portion of the subframes may not be destined for the station. Therefore, when a station in one multicast group receives an MU-PPDU frame containing a subframe destined for it and a multicast subframe not be destined for it, the receiving station may still need to decode the multicast subframe. This unnecessarily increases the time to process the MU-PPDU frame and increases power usage of the receiving device.